FILE - In this May 19, 2017, file photo, WikiLeaks founder Julian Assange greets supporters from a balcony of the Ecuadorian embassy in London. (AP Photo/Frank Augstein, File)
WikiLeaks founder Julian Assange will not willingly travel to the US to face charges filed under seal against him, one of his lawyers said, foreshadowing a possible fight over extradition for a central figure in the US special counsel’s Russia-Trump investigation.

Assange, who has taken cover in the Ecuadorian Embassy in London, where he has been granted asylum, has speculated publicly for years that the Justice Department had brought secret criminal charges against him for revealing highly sensitive government information on his website.

That hypothesis appeared closer to reality after prosecutors, in an errant court filing in an unrelated case, inadvertently revealed the existence of sealed charges. The filing, discovered last Thursday, said the charges and arrest warrant “would need to remain sealed until Assange is arrested in the criminal complaint and can therefore no longer evade or avoid extradition”.

A source, speaking on condition of anonymity, confirmed that charges had been filed under seal. The exact charges Assange faces and when they might be unsealed remained uncertain.

Any charges against him could help illuminate whether Russia co-ordinated with the Trump campaign to sway the 2016 presidential election.

They would also suggest that prosecutors have finally taken a more aggressive tack against WikiLeaks.

A criminal case can also potentially expose the practices of a radical transparency activist, under US scrutiny for years and at the centre of some of the most explosive disclosures of stolen information in the last decade.

Those include thousands of military and State Department cables from Army Private Bradley (now Chelsea) Manning, secret CIA hacking tools, and most recently and notoriously, Democratic emails published in the weeks before the 2016 presidential election and that US intelligence officials say had been hacked by Russia.

Federal special counsel Robert Mueller, who has already charged 12 Russian military intelligence officers with hacking, has been investigating whether Trump associates had advance knowledge of the stolen emails.

Assange could be an important link for Mueller to establish how WikiLeaks came to receive the emails, and why their release - on the same day a highly damaging video of Trump from a decade earlier surfaced publicly - appeared timed to boost his campaign.

Assange, 47, has been in the Ecuadorian Embassy under a grant of asylum for more than six years to avoid being extradited to Sweden, where he was accused of sex crimes, or to the US, whose government he has repeatedly humbled with mass disclosures of classified information.

The Australian was once a welcome guest at the embassy in London. But his relationship with his hosts has soured amid reports of espionage, erratic behaviour and diplomatic unease.

Barry Pollack, a Washington lawyer for Assange, expected Ecuador to “comply with its obligations” to preserve asylum for him, but acknowledged a concern that the county could revoke his asylum, expel him from the embassy and extradite him to the US.

“The burden should not shift to Mr Assange to have to defend against criminal charges when what he has been accused of doing is what journalists do every day,” Pollack said.

“They publish truthful information because the public has a right to know and understand what its government and institutions are doing.”

The charges came to light in an unrelated court filing from a federal prosecutor in Virginia, trying to keep sealed a separate case involving a man accused of coercing a minor for sex.

The filing contained two references to Assange, with one saying “due to the sophistication of the defendant and the publicity, no other procedure is likely to keep confidential the fact that Assange has been charged”.

It was not immediately clear why Assange’s name was included in the document. Joshua Stueve, a spokesman for the Justice Department’s Eastern District of Virginia said: “The court filing was made in error.”

The filing was discovered by Seamus Hughes, a terrorism expert at the Program on Extremism at George Washington University, who posted it on Twitter hours after The Wall Street Journal reported the Justice Department was preparing to prosecute Assange.

The case at issue concerns Seitu Sulayman Kokayi, a teacher, 29, indicted on charges of enticing a girl, 15, to commit sex acts and to produce child pornography. There doesn’t appear to be any connection between Assange and Kokayi.

The since-unsealed document, a motion filed in August asking to keep Kokayi’s case secret, mentions Assange twice, suggesting a copy-and-paste error or that his name was inadvertently in a template used for the filings.

The filing suggests prosecutors have reason to believe they will be able to arrest and extradite Assange.

Ecuadorian officials have cut off his high-speed internet access and will restore it only if he agrees to stop interfering in the affairs of Ecuador’s partners, such as the US and Spain. He is allowed to use the embassy’s wi-fi. Officials have also imposed a series of other restrictions on Assange’s activities and visitors.

Carlos Poveda, Assange’s lawyer in Ecuador, suspects Ecuador has been manoeuvring to kick Assange out through the stricter requirements recently imposed. He said possible US charges, however, are proof his client remains under threat, and he called on Ecuador’s government to uphold Assange’s asylum protections. He said Ecuador would be responsible if anything happened to Assange. AP African News Agency (ANA)